I may be able to get 300mm brackets.. so i could just machine them down?
Well.... NO.
Projection of the adapters fixing screw holes and the caliper fixing bolts intercept. The distance between the screw axis and the Brembo seating surface is 21mm on the 300 adapter which leaves enough meat to thread a hole and use a bolt (21 - 6 (half a M12 screw) = 15mm of thread available for the bolt, less about 1 or 2mm unthreaded of the bottom of the hole depending on the tap ). For 280 setup, the distance needs to be 10mm less (MartinR, 20mm on the diameter = 10 mm on the radius) which is generally done by 5mm off the adapter and 5mm off the caliper which would only leave about 8mm for the usable thread on the adapter which is way too short for a secure fitting that's why the 280 setup use studs rather than bolts for fixing the caliper.
One could think that if the caliper was machined 10mm instead of 5, it would fit the 300mm adapter. Yes it could but there a risk it may decrease wall thickness of the oil passages in the caliper too much (no one has a blueprint of the Brembo internals to make sure it's OK). Reducing 300 adapter 10mm is out of question obviously.
Archtronics, you will need min 5mm spacers (7mm better) when using Brembo with the 182 alloys to clear the spokes;